Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation Plans (Details Textuals)

v3.2.0.727
Stock-Based Compensation Plans (Details Textuals) - USD ($)
shares in Millions, $ in Millions
12 Months Ended
May. 31, 2015
May. 31, 2014
May. 31, 2013
Stock Based Compensation Plans (Textual) [Abstract]      
Number of shares authorized for issuance under stock plan 39.1    
Shares available for future grants 18.6    
Stock-based compensation expense $ 31.4 $ 26.3 $ 22.8
Income tax benefits related to stock-based compensation 11.7 $ 10.1 $ 8.5
Total unrecognized compensation costs related to all unvested stock-based awards $ 58.1    
Weighted-average period in years of all unvested stock-based awards 2 years 10 months 25 days    
Contractual life of stock option grants 10 years    
Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Options outstanding, Ending balance, Shares 4.7 5.4  
Performance Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Options outstanding, Ending balance, Shares 2.7 2.8  
Director [Member] | Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 1 year    
Director [Member] | Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 1 year    
Officer [Member] | Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting percentage 25.00%    
Officer [Member] | Performance Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Achievement of performance targets for fiscal 2014 23.50%    
Officer [Member] | Unearned Performance Shares [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Performance period for unearned performance shares 2 years    
Vesting period 1 year    
Officer [Member] | Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting percentage 33.00%    
Management [Member] | Restricted Stock Unit [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting percentage 20.00%    
Vesting period 5 years